AP Bio Lesson 2.1 Cell Structure and Function

AP Bio Topic 2.1

• 2.1 Cell Structure and Function

• ​2.1: Explain the basic ideas of the cell theory

  • Cells are the basic units of life, all living things are made of cells, and cells come from other cells.

• Compare and contrast the basic features of prokaryotic and eukaryotic cells.

• Describe the structure and functions of the following cell parts: nucleus, cytoplasm, cell membrane, ribosomes

• Endomembrane System: Rough endoplasmic reticulum, Smooth endoplasmic reticulum, Golgi complex, lysosomes, mitochondria, vacuoles, chloroplasts, cell wall

The Cell Theory

• The Core Tenets:

  • Cells are the basic unit of life: the simplest collection of matter that can be alive.

  • All living things are composed of one or more cells.

  • All cells come from pre-existing cells through cell division.

• Studying cells is the same as studying life.

Parts ALL Cells Have

• Cytoplasm

• Ribosomes

• Genetic Material

• Cell Membrane

• Cytoskeleton*

​An organelle is a cell part with a specific function

not one of the "big four"

Cytoskeleton

Structure:

• network of structural protein fibers (microtubules, microfilaments, and intermediate filaments) extending throughout the cytoplasm.

Function:

• Support: Helps cell maintains its shape; important for animal cells, which lack a cell wall.

• Transport vesicles move along cytoskeletal fibers, such as moving from the ER to the Golgi complex.

• Anchors: Ensures that organelles and enzymatic reaction sites are held in fixed, optimized locations within the cytosol.

• Cell movement via cilia or flagella; Movement of components in the cell via cytoplasmic streaming

Multiple Choice

Which of the following claims best supports the role of the cytoskeleton in cellular function?

• It provides a double membrane to separate metabolic reactions.

• It acts as a structural framework for cell shape and the movement of vesicles.

• It is the primary site for the synthesis of ribosomal RNA.

• It regulates the movement of water across the plasma membrane.

Multiple Choice

A researcher treats an animal cell with a chemical that prevents the assembly of microtubules, a primary component of the cytoskeleton. Which of the following cellular processes will be most directly inhibited by this treatment?

• The synthesis of ribosomal RNA (rRNA) and the assembly of ribosomal subunits in the nucleolus.

• The movement of transport vesicles from the rough endoplasmic reticulum to the Golgi complex.

• The chemical modification and glycosylation of new cellular products within the Golgi sacs.

• The maintenance of turgor pressure and storage of nutrients within a large central vacuole.

Cytoplasm

Structure:

• A semi-fluid jelly-like substance (cytosol) that fills the interior of the cell

Function:

• Provides a medium (place) for metabolic reactions to occur

• Suspends organelles and facilitates the movement of materials via cytoplasmic streaming

Multiple Choice

A researcher is comparing a bacterial cell and a plant cell. Both cells possess a semi-fluid, jelly-like substance that fills the interior and provides an aqueous medium for metabolic reactions to occur. Which of the following best describes the role and presence of this substance?

• It is the cytoplasm, which is found only in prokaryotic cells to protect DNA that is not enclosed in a nucleus.

• It is the cytoplasm, a universal component that facilitates the suspension of organelles and the movement of materials.

• It is the cytosol, which serves as the primary location for the chemical modification and folding of proteins.

• It is the stroma, a specialized substance found in all eukaryotic cells to maintain turgor pressure.

Ribosomes

Structure:

• made ribosomal RNA (rRNA) and proteins; non-membrane bound

Function:

• Synthesize proteins (assembling amino acids into polypeptide chains) through process of translation:

  • translate the genetic code from mRNA into primary polypeptide chains.

Evolution: Found in all forms of life, reflecting common ancestry of all organisms.

Multiple Choice

Ribosomes are composed of which two types of organic molecules?

• DNA and lipids

• Amino acids and fatty acids

• Carbohydrates and nucleic acids

• RNA and proteins

Multiple Choice

Which of the following best describes the primary function of ribosomes in all living cells?

• Synthesizing lipids for the plasma membrane.

• Storing genetic information for cellular replication.

• Translating mRNA sequences into polypeptide chains.

• Packaging proteins into vesicles for secretion.

Ribosome Location

• Bound Ribosomes: produce proteins for membrane insertion or secretion; attached to the Rough ER;

• Free Ribosomes: produce proteins that function within the cytosol (cytoplasm - intracellular); NOT attached to the Rough ER;

Multiple Choice

A cell is specialized for secreting large amounts of insulin (a protein hormone) into the bloodstream. Which of the following would you expect to see in high abundance in this cell?

• Free-floating ribosomes in the cytoplasm

• Ribosomes bound to the Rough Endoplasmic Reticulum

• Ribosomes located within the smooth ER

• Ribosomes located inside the central vacuole

​Genetic Material

Function:

• DNA houses the primary genetic code—the instructions for building every protein the cell needs to function, grow, and reproduce.

• DNA is a template used to make mRNA

  • mRNA is a template for translation for ribosomes

• Common Ancestry: DNA is the universal genetic material in all forms of life

Multiple Choice

The function of DNA in both cell types is to provide a template for the synthesis of which molecule?

• Messenger RNA (mRNA)

• Glucose

• Adenosine triphosphate (ATP)

• Phospholipids

Plasma (cell) Membrane (gatekeeper)

Structure:

• phospholipid bilayer with embedded proteins, steroids (cholesterol), glycolipids, and glycoproteins that surrounds the cytoplasm of a cell

Function:

• a selectively permeable barrier that regulates (controls) what enters and exits the cell to maintain homeostasis

Multiple Choice

Which of the following best describes the functional role of the plasma membrane in both prokaryotic and eukaryotic cells?

• It acts as a structural boundary that prevents the cell from bursting when placed in a hypotonic environment.

• It establishes and maintains a distinct internal environment by regulating the exchange of materials with the external environment.

• It provides a folded internal surface area specifically designed to increase the efficiency of ATP synthesis.

Match

Match the following functions.

• Controls what enters and leaves a cell

• Stores genetic information to make proteins

• Assembles amino acids into polypeptides (proteins)

• Provides a place for chemical reactions to occur

cell membrane

genetic material

ribosomes

cytoplasm

• cell membrane

• genetic material

• ribosomes

• cytoplasm

Multiple Choice

Which 4 parts do all cells have?

• cell membrane, mitochondria, DNA, ribosomes

• cell membrane, mitochondria, cytoplasm, DNA

• cell membrane, DNA, ribosomes, cytoplasm

• cytoplasm, DNA, ribosomes, mitochondria

Structures for Support and Movement:

• Cytoskeleton*

• Cell Wall

• Cilia

• Flagella

• Pseudopodia

Cell Wall

• Structure:

  • Plants: cellulose

  • Fungi: chitin

  • Bacteria / Archaea: peptidoglycan

• Function:

  • a structural boundary (it is permeable so it does not regulate like the cell membrane)

  • protection against osmotic lysis (bursting in hypotonic environments).

Cellulose made of Beta Glucose Molecules

Multiple Choice

Type I cells burst when placed in distilled water, while Type II cells swell but remain intact. Which of the following is the most likely explanation?

• Type II cells have a cell wall that provides structural support against hypotonic pressure.

• Type I cells have more mitochondria than Type II cells.

• Type II cells have a more permeable plasma membrane.

• Type I cells use active transport to pump water into the cell.

Cilia

Structure:

• short, hair-like projections made of proteins extending from the surface of the cell

Function:

• Used for locomotion like for protists like the paramecium

• Used to move fluids over the cell surface

• cilia increase the surface area of a cell to facilitate the exchange of materials with the environment

Flagella

• Structure:

  • Long, whip-like tails made of protein

• Function:

  • Locomotion (cell movement) certain protists and many bacteria, specialized eukaryotic cells (like sperm cells) , and simple eukaryote protists like euglena

Pseudopodia

Structure:

• Temporary, finger-like extensions of the cytoplasm and cell membrane formed through the rapid assembly and disassembly of microfilaments (actin filaments) in the cytoskeleton

Function:

• Locomotion (movement) of certain unicellular eukaryotes (like amoebas)

• Capturing food through endocytosis

Multiple Choice

Which of the following best explains how cilia and pseudopodia differ in their contribution to cellular function?

• Cilia are used primarily for genetic exchange, while pseudopodia are used for protein synthesis.

• Cilia increase surface area for absorption or movement, while pseudopodia are temporary extensions used for movement and engulfing food.

• Cilia are found only in prokaryotes, while pseudopodia are found only in plant cells.

• Cilia require ATP for function, while pseudopodia move via passive diffusion.

Centrosome:

• Structure:

  • microtubule proteins

• Function:

  • microtubules are organized (the Microtubule Organizing Center or MTOC).

• In animal cells, this contains the centrioles

Centrioles

• Structure:

  • cylindrical microtubules

• Function:

  • control spindle fibers during cell division (mitosis)

Membrane-Bound Organelles

• Nucleus

• rough ER

• smooth ER

• Golgi Apparatus

• Peroxisome

• Lysosome

• Vacuole

• Contractile Vacuole

• Mitochondria

• Chloroplasts

​Nucleus (boss, Mayor's office)

Structure:

• nuclear envelope (double-membrane - inner and outer)

• Nuclear pores (holes)

• nucleolus (rRNA synthesis = makes ribosomes)

• chromatin / chromosomes (DNA wrapped around histone proteins)

Function:

• genetic control center

• compartment to protect DNA instructions for protein synthesis

• Compartment that separates transcription (making mRNA) from translation (making proteins)

• Compartment that separates enzymes for DNA replication and RNA synthesis

• Nuclear pores regulate what enters and leaves nucleus

Rough ER (rER, rough endoplasmic reticulum - assembly line)

Structure:

• Network of membrane tubes/sacs studded with ribosomes attached.

Function:

• Folded membrane structure helps maintain cell organization and shape

• Compartment space (lumen) for folding and modifying proteins (protein synthesis)

• ensures proteins destined for secretion or membrane insertion don't get lost or clumped together in the cytoplasm

• Check if proteins are correct before they leave rER

Smooth ER (sER, smooth endoplasmic reticulum)

Structure:

• Network of membrane tubes (no ribosomes).

Function:

• compartment for enzymes that make lipids (lipid synthesis)

• compartment that keeps hydrophobic lipids separate from the water-based cytosol

• compartment for enzymes that modify toxins so they can be excreted (detoxification)

• Stores calcium ions keeping calcium levels low

• Breaks down glycogen into glucose (especially in the liver)

Multiple Choice

A cell from the liver is observed to have an unusually high concentration of Smooth Endoplasmic Reticulum. Which of the following is the most likely functional explanation for this observation?

• The cell is primarily responsible for the secretion of digestive enzymes.

• The cell is actively engaged in the detoxification of metabolic wastes or drugs.

• The cell requires high levels of ATP to move against a concentration gradient.

• The cell is storing genetic information for rapid cell division.

Multiple Choice

Individuals who frequently consume alcohol often show an increase in the amount of smooth ER in their liver cells. This change most likely helps the cell by:

• Increasing the rate of protein modification.

• Enhancing the efficiency of cellular respiration.

• Improving the cell's ability to detoxify chemicals.

• Storing more genetic information to replace damaged DNA.

Golgi Apparatus (Golgi complex, Golgi body - post office)

Structure:

• series of cisternae (flattened membrane sacs)

  • each sac (compartment) is like a different station on an assembly line

• Cis face receives vesicle from ER

• Trans face sends vesicle away (to be used in the cell or exported out of the cell)

Function:

• folds, chemically modifies, package, and sort the proteins they receive from the rER and place in vesicles for secretion

  • glycolsyation: adds or removes sugars from proteins

  • phosphorylation: adds phosphate groups to proteins

Multiple Choice

A cell is treated with a drug that prevents the Golgi apparatus from functioning. Which of the following processes will be most directly affected?

• The synthesis of proteins on free ribosomes.

• The detoxification of metabolic by-products in the smooth ER.

• The chemical modification and packaging of proteins for secretion.

• The production of ATP via aerobic cellular respiration.

Lysosomes (recycling center)

Structure:

• membrane enclosed sacs containing hydrolytic enzymes and an acidic pH of 5.0

Function:

• phagocytosis (intracellular digestion)

• autophagy (recycling materials)

• apoptosis (programmed cell death)

• Forms a compartment for enzymes that will not function in the pH of the cytosol/cytoplasm

Multiple Choice

Which of the following contains hydrolytic enzymes?

• lysosome

• vacuole

• mitochondrion

• Golgi apparatus

• peroxisome

Multiple Choice

Gaucher disease is a disorder where cells cannot break down specific lipids, leading to accumulation in tissues. This disease is most directly caused by a defect in which organelle?

• Smooth ER

• Lysosome

• Mitochondria

• Golgi Apparatus

Peroxisome

Structure:

• Membrane-bound sac containing enzymes (catalase).

Function:

• Breaks down fatty acids

• Detoxifies substances by transferring hydrogen from them and producing hydrogen peroxide (H₂O₂) which is then converted to water so it does not damage the cell

Multiple Choice

Peroxisomes contain enzymes that transfer hydrogen from various substrates to oxygen, producing hydrogen peroxide (H2O2) as a byproduct. Why is it essential that these reactions are compartmentalized?

• To prevent H2O2 from damaging other cellular components before it is broken down.

• To ensure that H2O2 can be used as an energy source for the mitochondria.

• To allow the H2O2 to be exported out of the cell for defense.

• To increase the rate of protein synthesis in the surrounding cytosol.

Vesicles

Structure:

• Temporary small membrane "bubbles" formed from budding of ER, Golgi, or cell membrane

Function:

• Compartment to transport materials within the cell between organelles

• Compartment to move molecules to the cell membrane to be secreted

Vacuoles (cabinets, warehouse)

Structure:

• Large membrane-bound sacs

Function:

• Temporary storage of water, waste, or food

• Plants:

  • stores water and ions

  • maintains turgor pressure (filled with water, pushes on cell wall to keep plant from wilting)

  • stores pigments to attract pollinators

  • stores toxins to deter herbivores

• Animals:

  • food vacuoles formed by phagocytosis merge with lysosomes so contents can be digested

Multiple Choice

A plant is placed in a hypertonic environment, causing it to wilt. This is most likely due to a change in which organelle?

• Chloroplast

• Central Vacuole

• Cell Wall

• Nucleus

Contractile Vacuole

Structure:

• membrane sac surrounded by a network of small canals

Function:

• Osmoregulation: constantly fills and empties with water to prevent cell from bursting

​SOME PROTIST CELLS

Multiple Choice

Researchers observe a single-celled eukaryote living in a freshwater environment. They notice that a specific organelle contracts more frequently when the cell is placed in a solution with lower salinity. Which of the following best explains this observation?

• The mitochondria are producing more ATP to move salt into the cell.

• The contractile vacuole is pumping out excess water that enters via osmosis.

• The lysosomes are breaking down salt crystals to maintain turgor pressure.

• The chloroplasts are increasing sugar production to reach equilibrium.

Multiple Choice

A paramecium is moved from a freshwater environment to a saltwater environment. Which of the following describes the most likely change in its contractile vacuole?

• The rate of contraction will increase to remove excess salt.

• The rate of contraction will decrease because less water is entering the cell.

• The vacuole will rupture due to the high external osmolarity.

• The vacuole will begin to store sugar to balance the external environment.

Mitochondria (powerhouse; site of ATP synthesis)- in all eukaryotic cells

• Structure: Double membrane; inner membrane is highly folded (cristae)

  • creates a compartment that increases the surface area to allow allows the mitochondrion to accumulate protons (H⁺) to high concentrations to build the electrochemical gradient needed for ATP production ATP to be synthesized more efficiently

• Function: Site of aerobic cellular respiration (converting energy stored in sugars into energy stored in ATP)

Mitochondria evolved from prokaryotes

• contain bacteria-like ribosomes (70s)

• have their own DNA that is circular and "naked" (lacks histones), just like bacterial DNA.

• inner and outer membrane

• reproduce independently by binary fission like bacteria

• Plant, animal, fungi, or protist cells

• Contain nucleus and membrane bound organelles (mitochondria, chloroplasts, ER, Golgi...)

EUKARYOTIC CELLS

• Bacteria & Archaea cells

• No nucleus or membrane bound organelles

PROKARYOTIC CELLS

Two Main Kinds of Cells

• Larger: 10-100 μm

• Unicellular: protists and some fungi

• Multicellular: plants, animals, most fungi

• Have compartments that allow them to grow larger and be more efficient by running many different metabolic processes at once

EUKARYOTIC CELLS

• Smaller: 1-5 μm

• Unicellular only: bacteria and archaea

• No compartments but have specialized internal membrane folds to perform specific functions

PROKARYOTIC CELLS

Categorize

Options (6)

Determine if the cells are prokaryotic or eukaryotic.

Prokaryotic (3)

Eukaryotic (3)

Match

Match the following

• Prokaryotic Cells

• Eukaryotic Cells

• All Cells

NO nucleus

Has a nucleus

cell membrane, ribosomes, DNA, cytoplasm

• NO nucleus

• Has a nucleus

• cell membrane, ribosomes, DNA, cytoplasm

​Prokaryote Genetic Material

• one single, circular chromosome found in the nucleoid region (not membrane-bound)

• sometimes have plasmids (extra-chromosomal loops of DNA)

• "naked" because it is not wrapped around histone proteins

Plasmid

Chromosome in Nucleoid

Cytoplasm

Cell Membrane

Ribosomes

Capsule

Cell Wall

Labelling

Label the prokaryotic cell.

Drag labels to their correct position on the image

plasmid

cell membrane

chromosome/DNA

ribosomes

cytoplasm

Multiple Choice

Small, extra-chromosomal loops of DNA often found in prokaryotes are called:

• Centromeres

• Plamids

• Nucleoli

• Cristae

Multiple Choice

A student is examining a single-celled organism under a microscope and observes that it possesses a cell wall but lacks a nuclear envelope. Based on these observations, which of the following groups could the organism belong to?

• Animals or Protists

• Plants or Fungi

• Bacteria or Archaea

• Eukaryotes only

​Eukaryote Genetic Material

• many linear chromosomes inside a membrane-bound nucleus

• DNA is wrapped around proteins called histones to keep it organized and compact.

• Compartmentalization: nuclear envelope allows for the separation of transcription (inside the nucleus) and translation (in the cytoplasm), increasing cellular efficiency

Chromosome

Cytoplasm

Cell Membrane

Ribosomes

Nucleus

Labelling

Label the eukaryotic animal cell.

Drag labels to their correct position on the image

ribosomes

nucleus

chromosome

cytoplasm

cell mem.

Multiple Choice

Which of the following describes a structural feature of genetic material that is unique to eukaryotes?

• The use of four nitrogenous bases (A, T, C, G) to store information.

• The presence of circular loops of DNA called plasmids.

• The wrapping of linear DNA around histone proteins to form chromatin.

• The ability of DNA to act as a template for messenger RNA.

Multiple Choice

Which of the following best describes a structural difference between the genetic material found in a bacterium and the genetic material found in a plant cell?

• The bacterium uses uracil instead of thymine in its primary genetic code, whereas the plant cell uses thymine.

• The bacterium’s DNA is organized into multiple linear chromosomes, while the plant cell's DNA is a single circular molecule.

• The bacterium contains a single circular chromosome in a nucleoid region, while the plant cell contains linear chromosomes within a nucleus.

• The bacterium wraps its DNA around histone proteins for stability, whereas the plant cell’s DNA is not associated with proteins.

Multiple Choice

Which statement accurately compares the structure of DNA in prokaryotes and eukaryotes?

• Prokaryotic DNA is usually a single circular molecule, while eukaryotic DNA is organized into multiple linear chromosomes.

• Prokaryotic DNA contains uracil instead of thymine, unlike eukaryotic DNA.

• Eukaryotic DNA is found in the cytoplasm, while prokaryotic DNA is sequestered in a nucleus.

• Prokaryotic DNA is wrapped around histone proteins, whereas eukaryotic DNA is "naked."

Multiple Choice

Which component is found in both the prokaryotic nucleoid and the eukaryotic nucleus?

• DNA

• rough ER

• nuclear pores

• a phospholipid bilayer

Multiple Choice

A researcher is studying two unknown cell samples, Sample A and Sample B, under an electron microscope.

Sample A contains cells with a single, circular chromosome and numerous small, non-membrane-bound structures in the cytoplasm.

Sample B contains cells with linear chromosomes enclosed within a double membrane and several specialized membrane-bound compartments, including one that contains highly folded inner membranes.

Which of the following claims is best supported by the researcher’s observations?

• Sample A is a eukaryotic cell because it contains ribosomes for protein synthesis.

• Sample B is a prokaryotic cell because the presence of a double membrane indicates a complex cell wall.

• Sample A is a prokaryotic cell because its genetic material is not sequestered within a nuclear envelope.

Open Ended

Prokaryotic and eukaryotic cells have some non-membrane-bound components in common, such as DNA and ribosomes.

(a) Describe the primary function of DNA within a cell.

(b) Explain ONE structural difference between prokaryotic DNA and eukaryotic DNA.

(c) Describe the primary function of ribosomes.

(d) Explain why both prokaryotic and eukaryotic cells must possess ribosomes, even though prokaryotes lack membrane-bound organelles.

• Have compartments that allow them to grow larger and be more efficient by running many different metabolic processes at once

EUKARYOTIC CELLS

• No compartments but have specialized internal membrane folds to perform specific functions

PROKARYOTIC CELLS

​​http://www.bozemanscience.com/017-compartmentalization

• Small or no vacuoles

• No cell wall

• No chloroplasts

• Centrioles help with cell division

• Lysosomes perform intracellular digestion

ANIMAL CELLS

• Large central vacuole

• Cell wall made of cellulose

• Chloroplasts make sugar by photosynthesis

• No centrioles

• No lysosomes

PLANT CELLS

​Animal Cells

• Centrioles: control spindle fibers during cell division (mitosis)

• Lysosomes: contain hydrolytic enzymes for intercellular digestion

Labelling

Label the animal cell parts.

Drag labels to their correct position on the image

DNA

Golgi

mitochondria

cytoplasm

cell membrane

nucleus

centrioles

rough ER

ribosomes

​Plant Cells

• Cell wall made of cellulose: protection and structure; prevents bursting

• Central vacuole: stores and releases water; maintains turgor pressure

• Chloroplasts: makes carbohydrates during photosynthesis

Labelling

Label the plant cell parts.

Drag labels to their correct position on the image

chloroplast

vacuole

cell wall

Topic 2.9: The Endomembrane System

• Define the term “endomembrane system,” and describe that system’s overall function. Descriptions should include:

  • Creating cellular compartments that segregate cellular functions such as hydrolysis, export of cell materials through exocytosis, import of materials through endocytosis, the capture of food or pathogens in phagocytosis, and assembly of macromolecules.

  • Creating compartments with optimal conditions for enzymatic reactions

  • Increasing surface area for membrane-bound enzymatic reactions (in the E.R. and Golgi).

• List the key membrane-bound organelles found within eukaryotic cells, and describe the structure and function of each.

  • The list should include rough E.R., smooth E.R., Golgi, lysosomes, vacuoles, vesicles, mitochondria, and chloroplasts.

• Explain how compartmentalization is different in eukaryotic and prokaryotic cells

  • Extensive compartmentalization is primarily a feature of eukaryotic cells.

  • Prokaryotic cells do have some internal compartments (such as the thylakoids in cyanobacteria)

Compartmentalization

Eukaryotes have membrane-bound compartments that makes them more efficient

• Separate chemical reactions, allowing them to occur simultaneously without interference

• Membrane folds increases surface area creates more "workspace" for membrane-bound enzymes reactions

• Compartments create ability to establish concentration gradients to pump ions or molecules into a confined space to build up potential energy used for cellular work

• Maintains internal conditions like pH inside the compartment for reactions to occur

The Endomembrane System

• System of organelles that work together to modify, package, and transport proteins, lipids, and polysaccharides

  • Nucleus

  • Rough ER

  • Smooth ER

  • Golgi Complex

  • Lysosomes

  • Vacuoles

  • Vesicles

​Nucleus (boss, Mayor's office)

Structure:

• nuclear envelope (double-membrane - inner and outer)

• Nuclear pores (holes)

• nucleolus (rRNA synthesis = makes ribosomes)

• chromatin / chromosomes (DNA wrapped around histone proteins)

Function:

• genetic control center

• compartment to protect DNA instructions for protein synthesis

• Compartment that separates transcription (making mRNA) from translation (making proteins)

• Compartment that separates enzymes for DNA replication and RNA synthesis

• Nuclear pores regulate what enters and leaves nucleus

Multiple Choice

Which of the following best explains how the compartmentalization of the nucleus contributes to the efficiency of eukaryotic cells?

• The nuclear envelope allows for the simultaneous occurrence of transcription and translation within the same interior space.

• The nucleolus serves as a specialized site for the synthesis of ribosomal RNA (rRNA) and the assembly of ribosome subunits.

• The double membrane of the nucleus provides a rigid structural boundary that prevents the cell from bursting in hypotonic environments.

• Nuclear pores act as unregulated channels that allow all cytoplasmic enzymes to freely interact with the genetic material at any time.

Rough ER (rER, rough endoplasmic reticulum - assembly line)

Structure:

• Network of membrane tubes/sacs with ribosomes attached.

Function:

• Folded membrane structure helps maintain cell organization and shape

• Compartment space (lumen) for folding and modifying proteins (protein synthesis)

• ensures proteins destined for secretion or membrane insertion don't get lost or clumped together in the cytoplasm

• Check if proteins are correct before they leave rER

Multiple Choice

Which of the following best describes how the structure of the rough endoplasmic reticulum (ER) supports its function in the endomembrane system?

• It lacks ribosomes, allowing it to specialize in the synthesis of lipids and the detoxification of metabolic waste.

• It contains high concentrations of hydrolytic enzymes that function at a low pH to recycle damaged cellular components.

• It is studded with bound ribosomes, providing a compartmentalized environment for the synthesis and folding of proteins destined for secretion.

• It features a highly folded inner membrane (cristae) that maximizes the surface area for the production of ATP via cellular respiration.

Smooth ER (sER, smooth endoplasmic reticulum)

Structure:

• Network of membrane tubes (no ribosomes).

Function:

• compartment for enzymes that make lipids (lipid synthesis)

• compartment that keeps hydrophobic lipids separate from the water-based cytosol

• compartment for enzymes that modify toxins so they can be excreted (detoxification)

• Stores calcium ions keeping calcium levels low

• Breaks down glycogen into glucose (especially in the liver)

Multiple Choice

The liver is involved in detoxification of many poisons and drugs. Which of the following structures is primarily involved in this process and therefore abundant in liver cells?

• rough ER

• smooth ER

• Golgi apparatus

• nuclear envelope

• transport vesicles

Golgi Apparatus (Golgi complex, Golgi body - post office)

Structure:

• series of cisternae (flattened membrane sacs)

  • each sac (compartment) is like a different station on an assembly line

• Cis face receives vesicle from ER

• Trans face sends vesicle away (to be used in the cell or exported out of the cell)

Function:

• folds, chemically modifies, package, and sort the proteins they receive from the rER and place in vesicles for secretion

  • glycolsyation: adds or removes sugars from protein

  • phosphorylation: adds phosphate groups to proteins

Multiple Choice

Which of the following best describes how the structure of the Golgi complex supports its specific function within the endomembrane system?

• Its physical continuity with the nuclear envelope allows for the direct transfer of mRNA to be translated into proteins.

• Its highly folded inner membrane (cristae) provides a large surface area for the enzymes involved in cellular respiration.

• Its arrangement of distinct, flattened membrane sacs (cisternae) allows for the sequential modification and sorting of proteins as they move through the organelle.

• Its lack of a membrane allows it to facilitate the rapid assembly of amino acids into primary polypeptide chains within the cytosol.

Ribosome > rough ER > Golgi > Cell Membrane

Lysosomes (recycling center)

Structure:

• membrane enclosed sacs containing hydrolytic enzymes and an acidic pH of 5.0

Function:

• phagocytosis (intracellular digestion)

• autophagy (recycling materials)

• apoptosis (programmed cell death)

• Forms a compartment for enzymes that will not function in the pH of the cytosol/cytoplasm

Multiple Choice

Which of the following contains hydrolytic enzymes?

• lysosome

• vacuole

• mitochondrion

• Golgi apparatus

• peroxisome

Multiple Choice

Hydrolytic enzymes must be segregated and packaged to prevent general destruction of cellular components. Which of the following organelles contains these hydrolytic enzymes in animal cells?

• chloroplast

• lysosome

• central vacuole

• peroxisome

• glyoxysome

Multiple Choice

If the membrane of a lysosome were to rupture, the hydrolytic enzymes would be released into the cytosol (pH ~7.2). These enzymes, however, are typically inactive at this neutral pH. This is an example of how the cell uses:

• Passive transport to regulate enzyme activity.

• Compartmentalization to create optimal local environments for reactions.

• Endocytosis to remove damaged organelles.

• Simple diffusion to move enzymes to their substrates.

Multiple Choice

The hydrolytic enzymes inside a lysosome function optimally at an acidic pH of approximately 5.0. However, the surrounding cytosol has a nearly neutral pH of approximately 7.2. Which of the following best describes the advantage of this compartmentalization?

• It allows the lysosome to produce ATP independently of the mitochondria.

• It protects the rest of the cell from self-digestion if a lysosome accidentally leaks or ruptures.

• It enables the lysosome to store genetic information separately from the nucleus.

• It increases the surface area-to-volume ratio of the cell, allowing for faster waste export.

Peroxisome

Structure:

• Membrane-bound sac containing enzymes (catalase).

Function:

• Breaks down fatty acids

• Detoxifies alcohol by producing hydrogen peroxide (H₂O₂) and then converting it into water.

Multiple Choice

A cell contains a specialized organelle that performs oxidative metabolism, specifically breaking down fatty acids and detoxifying harmful substances. This process results in the production of hydrogen peroxide (H²O₂), which is then safely neutralized by the enzyme catalase within the same compartment. Which organelle is being described?

• smooth ER

• lysosome

• peroxisome

• Golgi apparatus

Vesicles

Structure:

• Temporary small membrane "bubbles" formed from budding of ER, Golgi, or cell membrane

Function:

• Compartment to transport materials within the cell between organelles

• Compartment to move molecules to the cell membrane to be secreted

Multiple Choice

Vesicles are essential components of the endomembrane system. Which of the following best describes their role in the production and release of a secretory protein?

• They provide the structural scaffold where ribosomes attach to translate mRNA.

• They chemically modify proteins by adding carbohydrate tags in the Rough ER.

• They transport the folded protein from the Rough ER to the cis face of the Golgi complex.

• They contain the genetic blueprints required to initiate protein synthesis in the nucleus.

Vacuoles (cabinets, warehouse)

Structure:

• Large membrane-bound sacs

Function:

• Temporary storage of water, waste, or food

• Plants:

  • stores water and ions

  • maintains turgor pressure (filled with water, pushes on cell wall to keep plant from wilting)

  • stores pigments to attract pollinators

  • stores toxins to deter herbivores

• Animals:

  • food vacuoles formed by phagocytosis merge with lysosomes so contents can be digested

Multiple Choice

Which of the following best describes the primary function of the large central vacuole in a plant cell?

• Synthesizing lipids and steroids for the cell membrane.

• Storing water and ions to maintain turgor pressure against the cell wall.

• Containing hydrolytic enzymes used for intracellular digestion.

• Converting light energy into chemical energy through photosynthesis.

Contractile Vacuole

Structure:

• membrane sac surrounded by a network of small canals

Function:

• Osmoregulation: constantly fills and empties with water to prevent cell from bursting

​SOME PROTIST CELLS

Energy Conversion Organelles

• Mitochondria

• Chloroplasts

Mitochondria (powerhouse; site of ATP synthesis)

• Structure: Double membrane; inner membrane is highly folded (cristae) and creates a compartment that increases the surface area to allow ATP to be synthesized more efficiently

  • Found in all euakaryotic cells

• Function: Site of aerobic cellular respiration (converting energy stored in sugars into energy stored in ATP)

Mitochondria evolved from prokaryotes

• contain bacteria-like ribosomes (70s)

• have their own DNA that is circular and "naked" (lacks histones), just like bacterial DNA.

• inner and outer membrane

• reproduce independently by binary fission like bacteria

Multiple Choice

A researcher is studying two different types of mammalian cells. Cell Type A has many mitochondria with highly convoluted inner membranes, while Cell Type B has fewer mitochondria with smoother inner membranes. Which of the following is the most likely conclusion about the two cell types?

• Cell Type A is specialized for the storage of hereditary information.

• Cell Type A has a higher metabolic demand for ATP than Cell Type B.

• Cell Type B is more efficient at capturing light energy than Cell Type A.

• Cell Type B has a greater surface-area-to-volume ratio to allow for faster diffusion.

Multiple Choice

The inner mitochondrial membrane is highly convoluted, forming numerous folds known as cristae. Which of the following best explains how this structural feature supports the organelle's function?

• It establishes a double-membrane boundary that protects mitochondrial DNA from hydrolytic enzymes in the cytosol.

• It increases the surface area available for the membrane-bound proteins and enzymes required for efficient ATP synthesis

• It provides a larger internal volume for the storage of glucose and other metabolic precursors for glycolysis.

• It allows the mitochondrion to capture and store light energy as chemical energy within the intermembrane space.

Multiple Choice

In the mitochondria, the enzymes of the Krebs cycle (citric acid cycle) are located in the matrix, while the electron transport chain is embedded in the inner mitochondrial membrane. Which statement best describes the advantage of this spatial organization?

• It allows the cell to perform transcription and translation simultaneously.

• It prevents the mitochondrial DNA from being damaged by high-energy electrons.

• It allows for the establishment of a proton gradient across the inner membrane to power ATP synthesis.

• It increases the volume of the intermembrane space to store more glucose molecules.

Chloroplasts

• Structure: Double membrane; contains thylakoid stacks (grana/granum).

  • Double membrane creates compartment that increases efficiency of energy capture

  • Thylakoids contain chlorophyll (green pigment used to capture light energy for light reactions of photosynthesis)

• Only found in plant and algae cells

• Function: Site of photosynthesis (sugar production).

Chloroplasts evolved from prokaryotes

• contain bacteria-like ribosomes (70s)

• have their own DNA that is circular and "naked" (lacks histones), just like bacterial DNA.

• inner and outer membrane

• reproduce independently by binary fission like bacteria

Multiple Choice

The thylakoid membranes within a chloroplast are organized into stacks called grana. Which of the following best explains the functional significance of this structural organization?

• It provides a large surface area for the pigments and proteins required for the light-dependent reactions.

• It allows for the compartmentalization of the enzymes needed for the Calvin-Benson cycle.

• It facilitates the movement of glucose directly into the mitochondria for cellular respiration.

• It creates a barrier that prevents the diffusion of oxygen out of the chloroplast.

Multiple Choice

Chloroplasts are specialized organelles found in plants and algae that feature a double-membrane envelope and internal stacks of membrane-bound structures. Which of the following statements best describes how the structure of the chloroplast contributes to its function?

• The absence of internal membranes maximizes the space available for the storage of linear DNA and ribosomes.

• The double membrane provides distinct compartments that allow for the various metabolic reactions involved in photosynthesis to occur.

• The smooth inner membrane is the primary site for the conversion of chemical energy into ATP for cellular work.

• The hydrolytic enzymes stored within the thylakoid stacks allow the organelle to digest large macromolecules for energy.

Multiple Choice

A certain chemical disrupts the ability of a plant cell to maintain a high concentration of protons (H+) within the thylakoid space of the chloroplast. This chemical would most directly interfere with which of the following processes?

• The synthesis of proteins by the ribosomes in the stroma.

• The absorption of light energy by chlorophyll in the grana.

• The conversion of light energy into chemical energy during the light-dependent reactions.

• The fixation of carbon dioxide into organic molecules during the Calvin-Benson cycle.

Multiple Choice

Which of the following correctly describes a structural similarity between mitochondria and chloroplasts that supports their role in energy transformation?

• Both contain highly folded internal membranes that increase the surface area for metabolic reactions.

• Both possess a single outer membrane that allows for the rapid exchange of gases with the environment.

• Both contain specialized pigments that capture kinetic energy from the movement of water.

• Both use the stroma as the primary site for the synthesis of complex carbohydrates.

​PRACTICE QUESTIONS

Drag and Drop

A researcher is studying two unknown cell samples, Sample A and Sample B, under an electron microscope.

Sample A contains cells with a single, circular chromosome and numerous small, non-membrane-bound structures in the cytoplasm.

Sample B contains cells with linear chromosomes enclosed within a double membrane and several specialized membrane-bound compartments, including one that contains highly folded inner membranes.

The non-membrane-bound structures found in both Sample A and Sample B are ​

Placeholder

. These structures are responsible for ​

Placeholder

. While Sample B has membrane-bound organelles that allow for , Sample A must perform all metabolic functions within the cytosol or at the plasma membrane.

Drag these tiles and drop them in the correct blank above

ribosomes

protein synthesis

nucleoli

Multiple Choice

How does the location of ribosomes differ between prokaryotic and eukaryotic cells?

• Eukaryotic cells can have ribosomes bound to the endoplasmic reticulum, whereas prokaryotic ribosomes are only free-floating.

• There is no difference in location, as both cell types only have ribosomes in the cytosol.

• Prokaryotic ribosomes are only found in the nucleoid, while eukaryotic ribosomes are only in the cytoplasm.

• Prokaryotic ribosomes are housed within a nuclear envelope to protect them from metabolic reactions.

Multiple Choice

All of the following are part of a prokaryotic cell except

• DNA.

• a cell wall.

• a plasma membrane.

• ribosomes.

• an endoplasmic reticulum.

Multiple Choice

Tay-Sachs disease is a human genetic abnormality that results in cells accumulating and becoming clogged with very large and complex lipids.

Which cellular organelle must be involved in this condition?

• the endoplasmic reticulum

• the Golgi apparatus

• the lysosome

• mitochondria

• membrane-bound ribosomes

Multiple Select

Which TWO plant cell organelles contains their own DNA and ribosomes?

• chloroplast

• vacuole

• mitochondrion

• peroxisome

• Golgi apparatus

Multiple Choice

Thylakoids, DNA, and ribosomes are all components found in

• vacuoles

• chloroplasts

• mitochondria

• lysosomes

• nuclei

Multiple Choice

What types of proteins are NOT synthesized in the rough ER?

• extracellular matrix proteins

• secreted proteins

• mitochondrial proteins

• plasma membrane proteins

• endoplasmic reticulum proteins